Surface tension method of and apparatus for separating immiscible liquids

ABSTRACT

An apparatus for separating a selected liquid from a second liquid in which the selected liquid is immiscible by a surface tension action utilizing a hollow liquid surface tension separator having a surface tension screen wall is described. The separator is filled with the selected liquid and the outer side of its surface tension screen is placed in contact with the body of immiscible liquids to be separated, such that each screen pore exposed to the second liquid of the body contains a liquid-liquid interface whose interfacial surface tension resists passage of the second liquid through the pore. A pressure differential, less than the critical pressure differential necessary to overcome the interfacial surface tension force acting across the pore, is established across the screen to drive the selected liquid only through the screen into the separator. The primary application of the invention involves the removal or recovery of oil from a water surface utilizing an oil recovery apparatus which floats on and in some cases is propelled along the water surface and is equipped with one or more surface tension liquid separators for extracting the oil from the water surface.

United States Patent [191 Bhuta et al.

[ 1 SURFACE TENSION METHOD OF AND APPARATUS FOR SEPARATING lClBLELIQUIDS Assignee:

Notice:

Filed:

Appl. N0.: 288,593

Inventors: Pravin G. Bhuta, Torrance; Robert L. Johnson, Marina Del Rey;Douglas J. Graham, Redondo Beach, all of Calif.

TRW Inc., Redondo Beach, Calif.

The portion of the term of this patent subsequent to Nov. 21, 1989, hasbeen disclaimed.

Sept. 13, 1972 Related US. Application Data Division of Ser. No. 50,640,June 29, 1970, Pat. No.

US. Cl 210/109, 210/137, 210/242,

2l0/D1G. 21 Int. Cl B0ld 21/00 Field of Search 210/23, 40, 242, DIG. 21,

References Cited UNITED STATES PATENTS 5/1949 Verner 2l0/DIG. 21 8/1956Van Dijck... 11/1960 Lee et a1 12/1967 Kosar et a1 Harrington.. Smith11] 3,831,756 l*Aug. 27, 1974 FOREIGN PATENTS OR APPLICATIONS 1,284,3634/1969 Germany 210/DIG. 21

Primary Examiner-Frank A. Spear, Jr. Assistant Examiner- Robert H.Spitzer Attorney, Agent, or Firm-Daniel T. Anderson; Donald R. Nyhagen;Jerry A. Dinardo [57] ABSTRACT An apparatus for separating a selectedliquid from a second liquid in which the selected liquid is immiscibleby a surface tension action utilizing a hollow liquid surface tensionseparator having a surface tension screen wall is described. Theseparator is filled with the selected liquid and the outer side of itssurface tension screen is placed in contact with the body of immiscibleliquids to be separated, such that each I screen pore exposed to thesecond liquid of the body containsa liquid-liquid interface whoseinterfacial surface tension resists passage of the second liquid throughthe pore. A pressure differential, less than the critical pressuredifi'erential necessary to overcome the interfacial surface tensionforce acting across the pore, is established across the screen to drivethe selected liquid only through the screen into the separator. Theprimary application of the invention involves the removal or recovery ofoil from a water surface utilizing an oil recovery apparatus whichfloats on and in some cases is propelled along the'water surface and isequipped with one or more surface tension liquid separators forextracting the oil from the water surface.

1 Claim, 12 Drawing Figures SURFACE TENSION METHOD OF AND APPARATUS FORSEPARATING IMMISCIBLE LIQUIDS This is a division, of application Ser.No. 50,640, filed June 29, 1970, now US. Pat. No. 3,703,463.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to the art of separating immiscible liquids and moreparticularly to an apparatus for separating immiscible liquids using asurface tension screen to selectively extract one of the liquids. Theinvention relates also to a surface tension oil recovery apparatus forremoving or recovering oil from a water surface.

2. Prior Art As will appear from the ensuing description, the surfacetension liquid separation apparatus of the invention may be utilized toseparate virtually any two immiscible liquids. The primary applicationof the invention, however, involves the removal or recovery of oil fromthe surface of water. For this reason, the invention will be disclosedin connection with such use.

Oil pollution of oceans, lakes, and rivers has. become a serious problemis many parts of the world. The major sources of such oil pollution areleakage from off-shore oil wells, wrecked oil tankers, and leakage andnormal discharge from ships, harbor oil handling facilities, and thelike. Such oil pollution not only causes costly damage to and destroysboth the beauty and utility of shore lines, boats, marine facilities,and the like, but also impairs the health of and quite often killsmarine life an water fowl.

A variety of techniques and devices have been proposed for removing suchsurface oil and, in some cases, recovering the oil for reuse. Up to thepresent time, however, none of these techniques and devices have beenplaced into widespread use owning to their impracticality, at least forlarge scale use, their cost, their incapability of operation in any butextremely calm water, and/or other deficiences. Accordingly, a definiteneed exists for an improved oil removal and recovery apparatus which isnot subject to the drawbacks of the existing techniques and devices. Inits more limited aspects, the present invention provides such animproved oil recovery apparatus. In its broader aspects, the inventionprovides a liquid separation apparatus which may be utilized forseparating virtually any two immiscible liquids.

SUMMARY OF THE INVENTION According to its broader aspects, the inventionprovides a liquid separation apparatus for separating, with a surfacetension liquid screening action, a selected liquid from a second liquidin which the selected liquid is immiscible. This surface tensionscreening action involves the use of a surface tension liquid separatorcontaining a chamber bounded at least in part by a surface tensionscreen wall which is preferably preferentially wetted by the selectedliquid. In operation of the liquid separation apparatus, the liquidseparator chamber is filled with the selected liquid, such that thelatter wets the screen. The outer side of the screen is placed incontact with the body of immiscible liquids. Under these conditions,each screen pore which is directly ex posed to the second liquid in theliquid body contains a liquid-liquid interface whose interfacial surfacetension resists passage of the latter liquid through the pore. On theother hand, each screen pore which is exposed directly to the selectedliquid in the liquid body is devoid of such a liquid interface.Accordingly, passage of the selected liquid through the pore is notresisted by interfacial surface tension force.

While the surface tension screen is thus in contact with the liquidbody, a regulated pressure differential is established across thescreen, in a direction tending to drive liquid through the screen intothe separator chamber. This pressure differential is continuouslymonitored and regulated by an automatic pressure regulating system whichmaintains the pressure differential at a level below the criticalpressure differential required to drive the second liquid through thescreen against the resistance of interfacial surface tension.Accordingly, any selected liquid in contact with the outer side of thescreen is driven through the screen into the separator chamber. On theother hand,passage'of the second liquid through the screen into theseparator is blocked by interfacial surface tension.

A more limited but highly important aspect of the invention is concernedwith an oil recovery apparatus for removing and recovering oil from thesurface of water. In this application, a surface tension oil-waterseparator is filled with oil and supported by means of a float, suchthat the separator floats at the water surface. The oil is pumped fromthe separator chamber into a collection chamber, as the screen pressureregulating system permits, thereby maintaining a pressure differentialless than the critical pressure differential required to force waterthrough the separator screen into the separator chamber. Accordingly,any oil which contacts the outside (waterside) of the screen is drawnthrough the latter into the separator chamber from which the oil ispumped to the collection chamber.

The preferred forms of the oil recovery apparatus embody a stillingbasin with a surface skimmer inlet through which surface water and oilenter the basin and an outlet through which water is discharged from thebasin. Contained within the stilling basin are one or more surfacetension oil-water separators for extracting oil from the water-oilmixture which enters the basin. Certain embodiments of the oil recoveryapparatus are designed for sweeping large areas of a water surface.These embodiments comprise essentially a floating oil recovery vesselequipped with a large stilling basin having a forwardly opening surfaceskimmer inlet and with propulsion means for propelling the oil recoveryvessel forwardly through the water in such a way to cause entrance ofsurface water and oil into the stilling basin through its skimmer inlet.Within the stilling basin are a number of surface tension oil-waterseparators for extracting oil from the water in the basin. This oil ispumped from the separators into an oil receiver or collection chamber,such as a trailing barge. One disclosed oil recovery vessel utilizes anarray of flat rectangular oil-water separators arranged edge-to-edge inrows extending lengthwise and crosswise of the stilling basin. Theseparators float on the water surface and are connected by flexiblecouplings in such a way that the separators may rise, fall, and rotaterelative to one another under the action of wave motion within thestilling basin. Another disclosed oil recovery vessel utilizes rotaryoil-water separation drums. These drums have an outer surface tensionscreen wall defining radial vanes about drum vanes to increase theresidence time of contact of the oil with the drums.

Other disclosed embodiments of the present oil recovery apparatus aredesigned to remain stationary on the water surface or to be propelled byhand about the surface with the aid of a pole, or the like, to permitsurface oil removal from confined spaces, such as under piers and thelike. These latter embodiments are equipped with pumping means forinducing flow of surface water and oil through the apparatus. I

An important feature of the invention which may be utilized to advantagein oil recovery operations in cold areas involves heating theoiladjacent to the surface tension screen to reduce its viscosity andthereby accelerate passage of the oil through the screen.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective view of a surface oil recovery vessel accordingto the invention with parts broken away for the sake of clarity;

FIG. 2 is a semi-diagrammatic section through the oil recovery vessel ofFIG. 1;

FIG. 3 is a plane view of the oil recovery vessel;

FIG. 4 is an enlarged section taken on line 4-4 in FIG. 3;

FIG. 5 is an enlarged section through screen pores which are externallyexposed to water;

FIG. 6 is an enlarged section through screen pores which are externallyexposed to oil;

FIG. 7 is a plane view of a modified oil recovery vessel according tothe invention;

FIG. 8 is an enlarged section taken on line 8--8 in FIG. 7;

FIG. 9 is a vertical section through a modified oil recovery apparatusaccording to the invention;

FIG. 10 is a horizontal section through a further modified oil recoveryapparatus;

FIG. 11 is an enlarged section taken on line ll-1]l in FIG. 10; and

FIG. 12 is a section through a modified surface tension oil-waterseparator according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 through 6 illustrate asurface tension liquid separation apparatus 10 according to theinvention for separating a selected liquid 12 from a liquid body 14containing a second liquid 16 which is immiscible. In this instance, theselected liquid 12 is oil, the second liquid 16 is water on the surfaceof which the oil floats, and the liquid body 14 is a lake, ocean, river,or the like. The illustrated apparatus is thus a surface oil recoveryapparatus for removing or recoverying oil from the surface of water.

The main oil-water separation means of the oil recovery apparatus 10 iscomprised of surface tension oilwater separators 18. Turning to FIG. 4,it will be observed that each separator 18 contains a chamber 20 boundedat one side, in this instance at its lower side, by a wall 22 comprisinga surface tension screen. When the separator 18 is conditioned foroperation, its chamber 20 is filled with the selected liquid to berecovered,

i.e. oil, such that the oil wets the screen. According to preferredpractice of the invention, screen 22 is constructed of a material whichis preferentially wetted by the selected liquid to be recovered. In thisregard, it is significant to note that liquid which is selected forrecovery by filling the separator chamber is preferably the one whichpreferentially wets the separator screen.

In the operation of the surface tension liquid separator 18, the outerside of its screen 22 is placed in contact with the body of water, asshown in FIG. 4. Under these conditions, each screen pore exposedexternally to water contains a liquid or oil-water interface 24 (FIG. 5)which separates the oil on the inside of thescreen from the water on theoutside of the screen. Each interface possesses an interfacial surfacetension which resists passage of the water through the pore into theseparator chamber 20. This interfacial surface ten sion blocks passageof the water through the pore under the action of a differentialpressure AP (water pressure greater than oil pressure in the separatorchamber 20) across the screen which is less than the critical pressuredifferential required to overcome the interfacial surface tension, i.e.required to drive the water through the pore against the interfacialsurface tension of the corresponding oil-water interface 24. Thiscritical pressure differential is determined by the interfacial surfacetension of the oil and water and by the characteristics, i.e. pore size,material, etc., of the surface tension screen 22. The critical pressuredifferential AP is represented by the equation:

where p is the total water pressure outside of the screen,

P is the oil pressure just inside the screen,

(T is the interfacial surface tension between water and oil,

r is the radius of the oil-water interface (i.e., the radius of theopening in the screen, and

K is a constant of proportionality having a value of approximately 2.0,depending on the type of screen.

In constrast, the screen pores which are exposed to oil on the outsideof the surface tension screen 22 contain no liquid interface, as may bereadily observed in FIG. 6. Accordingly, passage of the oil through thescreen into the separator chamber 2 is not resisted by interfacialsurface tension. The pressure differential maintained across the screenby the pressure regulating system thus drives the oil through the screeninto the separator chamber 20.

From the foregoing discussion, it will be understood that if a pressuredifferential AP less than the critical pressure differential AP isestablished across the surface tension screen 22 of the oil-waterseparator 18, only oil in contact with the outer surface of the screenwill pass through the screen into the separator chamber 20. Passage ofwater through the screen is blocked by the interfacial surface tensionof the oil-water interfaces 24. I

Returning now to the oil recovery apparatus 10, the latter comprises afloating oil recovery vessel having a relatively large stilling basin 26supported by float means 28 such that the basin floats at the surface ofthe water from which the surface oil is to be recovered. In thisinstance, the float means 28 comprise pontoons or catamaran hulls whichstraddle the stilling basin and are attached to the basin by struts 32.Contained within the stilling basin 26 is a relatively large stillingchamber 34. The forward end of the basin is necked down to form an inletdiffuser throat 36. The diffuser passage within the throat opensrearwardly to the stilling chamber 34 and forwardly to a surface skimmerinlet 38. This inlet projects a distance above and below the normalwater line level of the stilling basin. A grill is placed across theinlet to block the entrance of sizable floating objects. A pair ofsurface skimming booms 41 extend forwardly from the inlet in divergingrelation to one another. At the rear end of the stilling basin is anoutlet 42 connected to the inlet of a pump 43.

Within the stilling chamber 34 is an array 44 of oilwater separators 18.Each separator has a relatively flat rectangular housing 46 (FIG. 4)with an open bottom side across which extends the separator surfacetension screen 22. Encircling each housing is a ring float 48 whichprovides the separator with positive bouyancy in water. The severalseparators 18 are arranged sideby-side in rows extending lengthwise andcrosswise of the stilling basin to form a rectangular separator arraywhich encompasses virtually the entire water surface area in thestilling chamber. The adjacent separators are joined by hinge means 50,in this instance fabric or plastic webs, which permit the separators torise, fall, and rotate relative to one another under the action of wavemotion in the stilling chamber.

Connected to the center of the upper wall of each separator housing 46is an axially and aterally flexible riser 52. The riser of the severalseparators in each axial separator now connect to a header 54. The rearends of the headers connect to a common flexible outlet conduit 55,connected to suction line 56 of a pump 58. The discharge line 60 of pump58 connects to a spout 61 which empties into an oil receiver 62. In thisinstance, the oil receiver is a large barge which is attached, by hingedvertically swingable links 64 to the rear end of the hulls 30. Pump 58,as well as the earlier mentioned stilling basin suction pump 43, aremounted on the front of the barge. The discharge of the basin suctionpump empties overboard.

During operation of the oil recovery apparatus or vessel 10, the latteris propelled forwardly through the water by suitable propulsion means.The particular oil recovery vessel illustrated has a propulsion engine68 at'the rear of the barge 62. Located over the engine is an operatorstation 70 equipped with means 71 for steering control, controlling theengine 68, and the pumps 43, 58.

As the oil recovery vessel 10 moves forwardly through the water, theskimmer booms 41 skim the water surface and convey any oil on thesurface toward and finally into the skimmer inlet 38. The surface waterand oil entering the inlet pass throughthe inlet diffuser throat 36 intothe stilling chamber 34. The inlet throat passage flares outwardly as itenters the chamber to diffuse the entering, relatively high velocitywater-oil stream to a relatively low velocity stream within the stillingchamber. Flow control and diffuser vanes 72 are mounted in the passageto aid this diffusing action and to damp wave motion. Water exits fromthe chamber through the chamber outlet 42 and the pump 43 whichdischarges the water overboard.

The oil-water separators l8 extract oil from the water within thestilling chamber 34. ln this regard, it will be understood that theseparators are intially filled with oil to condition them for theirearlier described surface tension oil-water separating or screeningaction. The separators are thus filled with oil through a filling system74 to be explained presently. Actual oil extraction operation of theseparators is initiated by operating the pump 58 to reduce the pressurewithin the separator chambers 20 and thereby produce across theseparator screens 22 the pressure differential required to induce oilpassage through the screen into the separator by the surface tensionoil-water separating screening action described earlier.

As noted in this earlier description, in order to induce passage of oilonly, and not water, into the separators,

the pressure differential across the separator screens 22 i must bemaintained less than the critical pressure dif ferential AP To this end,the oil recovery vessel 10 is equipped with an automatic pressurecontrol system 76 for continuously monitoring the pressure differentialacross the separator screens and regulating the separator pumping actionto maintain the proper pressure differential across the screens. Theparticular control system illustrated comprises a differential pressuretransducer 78 mounted within the stilling chamber 34. This transducer isexposed, through a tube 80, to the water pressure on the outside of theseparator screens, and through a flexible tube 82, to the oil pressureon the inside of the screen of an adjacent separator 18. The lower openend of pipe 80 is submerged to a depth sufficient to avoid uncovering ofthis end by wave motion. Electrically connected between the transducer78 and a solenoid proportioning valve 84 in the pump suction line 56 isa valve control unit 86. Leading from the suction line 56, at a pointbetween the valve 84 and pump 58,'is an intake line 88 which opens tothe bottom of the oil collection chamber in the barge 62.

The transducer 78 senses the water pressure on the outside of theseparator screens 22 and the oil pressure on the inside of the screen ofthe adjacent separator and generates an electrical signal representingthe difference between these pressures. The control unit 86 operates theproportioning valve 84 in response to this electrical signal toproportion flow through the lines 56, 88 in such a way as to maintainthe screen pressure differential at the proper level to accomplish theoilwater separating action. Thus, the control unit 86 responds to aprogressively increasing pressure differential across the screens 22 byprogressively closing the proportioning valve 84. Under theseconditions, oil flow from the separators 18 is progressively reduced andthe oil flow through that part of the oil recirculating loop comprisingcollection chamber 90, and that part of the intake line 88 before thepoint where line 56 joins 88, is correspondingly increased. The internalpressure in the separators 18 is thereby reduced. Conversely, thecontrol unit 88 responds. to a progressively diminishing pressuredifferential across the separator screens 22 by progressively openingthe proportioning valve 84 to increase the oil flow from the separatorsand reduce the circulating oil flow through that part of theoilcirculating loop comprised of 90 and that part of 88 before the pointwhere line 56 joins 88. The internal pressure in the separators isthereby increased. The control system 76 is adjusted to maintain theselected pressure differential across the separator screens 22. In thisregard, it is significant to note that the control system maintains theproper pressure differential regardless of the presence or absence ofoil in contact with the outer surface of the separator screens.

From the description to this point, it will be understood that the oilrecovery apparatus or vessel 10 is effective to extract from the waterin the stilling chamber 34 any oil which enters into contact with theseparator screens 22 and to collect the oil in the barge collectionchamber 90. The only remaining requirement for efficient operation ofthe oil recovery vessel 10, therefore, involves contacting the incomingoil with the separator screens. This is accomplished by an inletdeflector 92 and bottom deflectors 94 within the stilling chamber 34.The inlet deflector 92 deflects the entering water and oil downwardly tothe bottom of the chamber, such that the oil then rises into contactwith the undersides of the separator screens. This upward motion of theoil into contact with the screens is aided by the bottom deflectors 94and by the diffusing action of the duffuser inlet throat 36 and vanes 72which slow the entering oil-water stream to increase the residence timeof the oil in the chamber. As noted earlier, water exits from thestilling chamber through the outlet 42 and the pump 43 which dischargesthe water overboard.

As noted earlier, the oil recovery vessel 10 has means 74 for initiallyfilling the separators 18 with oil, thus to condition the same for theiroil-water separating action. The particular filling means showncomprises a fill line 96 connecting the suction and discharge lines 5 6,60 of the pump 58, and two-way valves 98 which may be set in normaloperating position and separator filling position. In their normaloperating position, these valves block the ends of the fill line 96 andconnect the pump intake to both the separators l8 and the intake line 88and the pump outlet to. the spout 61. The apparatus is then conditionedfor the described oil recovery operation. In filling position, valves 98connect the pump intake to the intake line 88 only and the pump outletto the separators 18, only, through the fill line 96. Under theseconditions, operation of the pump 58 draws oil from the barge 62 throughthe intake line 88 and delivers the oil to the separators 18 through thedischarge line 60, fill line 96, and separator headers 54.

The modified surface oil recovery apparatus or vessel 100 of FIGS. 7 and8 has a stilling basing 102 supported by stradlling pontoon floats orcatamaran hulls 104.

The stilling basin 102 contains a stilling chamber 106 which opensforwardly through an inlet diffuser throat I08 terminating in a surfaceskimmer inlet I10. Within the throat passage are flow control anddiffuser vanes 112. Surface skimmer booms I14 extend forwardly indiverging relation from the inlet. Attached to the rear ends of thehulls 104, by hinged vertically swingable links 116, is an oilcollection barge 117. At the rear end of the stilling basin 102 is anoutlet 118 connected to a suction pump 119 on the barge. The oilrecovery vessel described to this point is thus generally similar tothat of FIGS. 1 through 6.

The modified oil recovery vessel I00 differs from that of FIGS. 1through 6 in the type of oil-water separators which are employed toextract oil from the water in the stilling chamber 106. In the modifiedapparatus, the oil-water separators 120 comprise rotary drums eachhaving an outer surface tension screen wall 122. This screen wall orscreen is shaped to form a number of hollow radial vanes 124circumferentially spaced about the drum. Extending centrally througheach drum is a tubular shaft 126. The ends of this shaft extend beyondthe ends of the drum and through the sidewalls of the stilling basin 102and the inner sidewalls of the hulls M14. The shaft ends are rotatablysupported in bearings 128 in the basin and hull walls and are sealed tothe hull walls in any convenient manner. Each separator drum 120 hasendwalls which are fixed to the respective shaft 126, such that theshaft and drum rotate in unison. The several separator drums arearranged side-by-side in the fore and aft direction of the stillingchamber 106 so as to occupy vitually the entire water surface area inthe chamber. The drums have their axes located in a common horizontalplane approximately at the normal water line level in the chamber.

Rotatably supported in and extending longitudinally through the lowerhull 104 in FIG. 7 is a drive shaft 130. This drive shaft is drivablycoupled by bevel gears 132 to the adjacent end of the separator drumshafts I26. Shaft is driven in rotation by a motor 134 to rotate theseparator drums 120 in the clockwise direction in FIG. 8. Therotationalspeed of the drums is relatively low, and may be on the orderof 3 rpm.

Extending centrally through each drum shaft 126 is a passge 136. Thispassage communicates to the interior of the respective separator drumchamber 138 throtfgh ports 140 in the shaft. The lower ends of the drumshaft 126 in FIG. 7 are sealed. The upper ends of the shafts in FIG. 7are connected by rotary seals 142 to a header 144 extendinglongitudinally through the adjacent hull 104. The drum shaft passages136 open to the interior passage in this header. The front end of theheader 144 is sealed. The rear end of the header extends rearward of thehull I04 and is connected to the suction line 148 of a pump 150 mountedon the barge I17. Pump 150 has a discharge line 152 connecting to aspout 153 which empties into the coil collection chamber 154 in thebarge. The barge has a rear engine and control station (not shown) likethe barge in FIGS. I through 6.

The oil recovery vessel 100 has filling means 156 for initially fillingthe separator drums 120 with oil. This filling means is essentiallyidentical to that of the oil recovery vessel It) and thus need not beexplained in detail. Suffice it to say that the filling means 156includes a fill line 158 connecting the pump suction and discharge lines1148, 152, a pump intake 159 opening to the bottom of the oil collectionchamber 154, and twoway valves 160 for placing the pumping system in thenormal operating and separator filling modes described earlier.

During operation of the oil recovery vessel 100, the barge engine isoperated to propel the vessel through the water and thereby induce flowof surface water and oil through the skimmer inlet 110 into the stillingchamber 106. The pump 119 is operated to discharge water overboard fromthe rear end of the stilling chamber. Pump 1150 is operated, with valves160 set in normal operating position, to pump oil from the separatordrums 120 and thereby establish across the drum screens 122 the pressuredifferential required to effect the earlier described surface tensionoil-water separating action. It will now be understood, therefore, thatthe oil-water recovery vessel 100 is effective to extract from the waterwithin stilling chamber 106 any oil which enters into contact with thedrum screens. The oil is pumped from the interior chambers 138 of theseparator drums 120 through the drum shaft ports 140,

9 shaft passages 136, and header 144 to the barge 117.

A feature of the oil recovery vessel 100 resides in the fact that theseparator drums 120 are driven in a clockwise direction of rotation inFIG. 8 by their drive motor 134 during the oil recovery operation. Thisdrum rotation achieves two benefits. First, drum rotation exposes theentire surface area of each drum screen 122 to the water and oil instilling chamber 106. The surface area of each drum screen, in turn, ismaximized by the vaned configuration of the screen. Thus, the totaleffective surface tension screen area of the oil recovery vessel ismaximized, thereby maximizing the oil recovery rate for a given stillingchamber area. Secondly, the rotating screen vanes 122 displace oil fromthe surface of the water in the stilling basin to the under sides of thescreens, where the oil rises upwardly along the vanes and is trapped inthat area between the vanes thereby retaining the oil in contact withthe screen. The vanes carry the oil around with the drum to increase theresidence time of the oil in contact with the screen drums.

Oil recovery apparatus 100 has a pressure control system 162 formaintaining the proper pressure differential across the separator drumscreens 122. This control system is essentially identical to that of theearlier oil recovery vessel 10 and need not be explained in detail,suffice it to say that the control system 162 comprises a pair ofpressure transducers 164, 166, a flow proportioning valve 168 in thepump suction line 148, the pump intake 159, and a control unit (notshown) for operating the valve 168 in response to the pressure signalsfrom the transducers to maintain the internal screen pressure at thelevel to establish the proper pressure differential across the drumscreens. Transducer 164 is mounted within and attached to the stationarymember of the rear drum rotary seal 142 to sense the pressure of the oilexiting from the rear separator drum 120. This oil pressure, of course,is slightly less than the oil pressure on the inner surface of the reardrum screen 122. Transducer 164 is calibrated and adjusted to compensatefor this pressure drop inthe oil from the screen to the transducer in amanner such that the transducer provides a pressure signal representingthe internal screen pressure of the rear drum. Transducer 166 is mountedwithin the stilling chamber 106, below the normal water line level inthe chamber, so as to provide apressure signal representing the externalwater pressure on the rear drum screen 122.

FIG. 9 illustrates an oil-water separator or surface oil recoveryapparatus 200 according to the invention which may be tethered to floatstationary in the water or may be attached to a pole, or the like, topermit movement of the apparatus by hand through confined areas underpiers and the like. Oil recovery 200 has a lower bowl 202 and a hollowtop plate 204 which together form a stilling basin. The perimeter ofbowl 202 is curled outwardly and downwardly to form a rim 206. The topplate 204 overlies the basin rim 206 to define an interveningannularsurface skimmer inlet 208. Plate 204 is attached to the basin rim 206 bystruts 210 which may serve as diffuser vanes. Bowl 202 and top plate 204define an intervening stilling chamber 211 communicating with theskimmer inlet 208. Surrounding the bowl 202, below its rim 206,is a ringfloat 212. This float and the void 214 within the top plate 204 providethe oil recovery apparatus with a positive buoyancy in water, such thatthe apparatus floats with the skimmer inlet 208 at water surface level.

Extending from the bottom of the bowl 202 is a tube 216 which is open atits lower end and provides an outlet passage 210 from stilling chamber211. Mounted along this outlet tube is a motor driven pump 220 having arotary driven impeller or the like (not shown) within the outlet passage218 for pumping water from stilling chamber through the passage. Thispumping action draws surface water and oil into the chamber through theskimmer inlet 208.

Sealed about its perimeter to the underside of the top wall 204 is asurface tension screen 222. Fixed to the underside of the wall withinthe screen is a conical wall member 224 which defines with the screen anarrow intervening separator chamber 226. An oil outlet tube 228 extendsupwardly from the center of the wall member 224 and through the topplate 204. This oil outlet tube connects to a pumping system (not shown)similar to those described earlier for pumping oil from and therebyreducing the pressure in the separator chamber 226 to produce apressuredifferential across the screen 222. As in the previous forms of theinvention, the pumping system connected to the oil outlet tube 228 iscontrolled by an automatic pressure control system for.

' maintaining across the screen the maximum pressure differential toachieve the earlier described oil-water separating action. This controlsystem is like those described earlier and includes a differentialpressure transducer 230 mounted on the underside of the top plate 204,adjacent the edge of the screen 222. The transducer is exposed to theinternal screen pressure through a tube 232 opening to the separatorchamber 226. The transducer is exposed to the external screen pressurethrough a tube 234 opening to the water on the outside of the screen.Transducer 230 generates an output signal representing the pressuredifferential across the screen. As described earlier, this pressuresignal is fed to the control unit of the pressure control system whichactuates the proportioning valve in the oil pumping system to maintainthe correct pressure differential across the screen 222.

In operation of the oil recovery apparatus 200, water pump 220 isoperated to induce flow of surface water and oil through the skimmerinlet: 208 into the stilling chamber 211. The shape of the chamber invertical cross-section will be seen to be such as to produce a diffusingaction which slows the entering stream and thereby permits contact ofthe oil with the screen 222. The oil is drawn through the screen intothe separator chamber 226 and is then pumped from this chamber throughthe outlet tube 228 to an oil receiver or collection chamber. The oilrecovery apparatus 200 may be tethered in a stationary position orattached to a pole or the like to permit the apparatus to be moved aboutthe water surface by hand and particularly through confined spaces, suchas under piers and the like.

The surface oil recovery apparatus 300 of FIGS. 10 and 11 comprises atubular surface tension oil-water separator 302 with surface tensionscreen side walls 304 and solid top and bottom walls 306. Attached atintervals to the separator are floats 308 which support the separator inwater in the position of FIG. 11. In this position, the separatorscreens 304 contact the surface water and oil. One end of the separator300 is closed. The other end of the separator is connected to thesuction line 310 of a pumping system like those described earlier.

In use, the separator 300 is placed in a surrounding relation to an oilslick or patch 312 on the waters surface. The pumping system is thenoperated to effect the surface tension oil-water separating actiondescribed earlier, whereby the oil is drawn into the separator throughthe screens 304 and is pumped to an oil collection chamber.

The oil recovery apparatus 300 is provided with an automatic pressurecontrol system like those described earlier for controlling the pumpingsystem to maintain the proper pressure differential across the submergedportions of separator screens 304. This control system includes adifferential pressure transducer 314 mounted in the bottom wall 306 ofthe separator for sensing internal and external screen pressures.

The decrease in oil collection rate due to a reduction in oiltemperature in attic regions or when collecting oil of high viscosity intemperature regions can be compensated for by placing a heat exchangerinside the surface tension screen separator to heat the oil and reduceits viscosity. FIG. 12, for example, shows such a heat exchanger 400within a present separator 18. Heat for the exchanger can be obtainedfrom any convenient source. In the present oil recovery vessels, forinstance, waste heat from the propulsion engine may be circulatedthrough a heat exchanger 402 disposed in heat transfer relation to aconduit 404 containing a pump 406 for recirculating a heat transferfluid, such as water, through the heat exchanger 400. The heat exchangeris arranged close to and preferably in direct contact with the surfacetension screen so as to support the screen. The oil is heated by theheat exchanger 400 and, since the oil is in intimate contact with thescreen, the screen is heated also. Any oil coming in contact with theoutside of the screen adheres to the screen since it is wetted with asimilar oil. Heat is thereby transferred to the oil on the outside ofthe screen thus reducing its viscosity and allowing the flow ratethrough the screen to be increased.

The parameters of the surface tension screens employed in the presentoil recovery apparatus may vary, depending upon the oil to be recovered.For California crude oil, suitable screen parameters are as follows:

Screen material stainless steel Screen pore size 50 X 250 mesh AP acrossscreen 2" H O (0.07 psi) What is claimed as new in support of LettersPatent 1s:

1. A device for removing from the surface of a body of water a liquidimmiscible with water and floating at said water surface, comprising:

a liquid separator assembly comprising a generally planar array ofseparate hollow flat rectangular liquid'separators each having a chamberbounded at one side by a screen wall;

hinge means joining the adjacent separators on hinge axes parallel tothe plane of the array with the screen walls of all the separatorslocated at the same side of the array;

float means on said separator assembly for floating the assembly in saidbody of water with said separator screen walls located at the undersideof the assembly at said water surface;

each separator being adapted to be initially filled with said liquid andhaving an outlet through which the liquid may be pumped from theseparator chamber to create a pressure differential across the separatorscreen wall for inducing passage of said liquid only from the watersurface into the separator chamber; and

means for sensing and producing an electrical signal representing saidpressure differential.

1. A device for removing from the surface of a body of water a liquidimmiscible with water and floating at said water surface, comprising: aliquid separator assembly comprising a generally planar array ofseparate hollow flat rectangular liquid separators each having a chamberbounded at one side by a screen wall; hinge means joining the adjacentseparators on hinge axes parallel to the plane of the array with thescreen walls of all the separators located at the same side of thearray; float means on said separator assembly for floating the assemblyin said body of water with said separator screen walls located at theunderside of the assembly at said water surface; each separator beingadapted to be initially filled with said liquid and having an outletthrough which the liquid may be pumped from the separator chamber tocreate a pressure differential across the separator screen wall forinducing passage of said liquid only from the water surface into theseparator chamber; and means for sensing and producing an electricalsignal representing said pressure differential.